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1.
Indian Ocean humpback dolphins Sousa plumbea inhabit nearshore waters from South Africa to eastern India. Humpback dolphins are vulnerable to conservation threats due to their naturally small population sizes and use of nearshore habitats, where human activities are highest. We investigated the abundance and residency of this species inhabiting Mossel Bay, South Africa, using photographic mark-recapture. Data were collected during 81 surveys in Mossel Bay between 2011 and 2013. Open population modelling using the POPAN parameterisation produced a ‘super-population’ estimate of 125 individuals (95% CI: 61–260) and within-year estimates of between 33 and 86 individuals (2011: 71 [95% CI: 30–168]; 2012: 33 [15–73], 32 [15–70]; 2013: 46 [20–108]). Although less appropriate, closed capture models were also run for comparison with previous studies in the region and generated similar, but slightly smaller, population estimates within each year. We compared our catalogue with opportunistic data collected from East London, Plettenberg Bay, De Hoop and Gansbaai. The only catalogue matches attained were between Plettenberg Bay (n = 44 identified) and Mossel Bay (n = 67 identified), separated by 140?km. Population exchange was moderate, with nine individuals resighted in multiple years between these two areas. This study supports previous findings of long-range movements for this species and provides a baseline from which to assess future impacts on the population. 相似文献
2.
The end of the Neoproterozoic is punctuated by glacial deposition, but the chronology of these deposits is hindered presently by the paucity of geochronological data. Here, we present new radiometric dating for the basal Sete Lagoas cap carbonate deposits that overlie glacial units in the São Francisco craton. Six samples from aragonite‐pseudomorph crystal‐rich facies, showing pristine textures and constant 87Sr/86Sr ratios around 0.7075, yielded a Pb–Pb isochron age of 740 ± 22 Ma, which is interpreted as the depositional age for these remarkably preserved rocks. This age can be used to infer a low‐to‐moderate palaeolatitude of 20–30° for carbonate (and glacial) deposition. In addition, as it overlaps the ages obtained for the oldest Neoproterozoic glacial successions, our result reinforces the idea of a long‐standing ‘Sturtian’ interval, suggesting that this event represents either different discrete glaciations or a protracted event encompassing almost 80 Ma. 相似文献
3.
Liliane Janikian Renato Paes De Almeida Ricardo Ivan Ferreira Da Trindade Antonio Romalino Santos Fragoso‐Cesar Manoel Souza D′Agrella‐Filho Elton Luis Dantas Eric Tohver 《地学学报》2008,20(4):259-266
The Ediacaran is one of the most important periods on Earth evolution, including the first appearance of soft‐bodied macrofossils, major climatic changes and a supposed rise in free oxygen. In southernmost Brazil, this period is represented by Camaquã Supergroup, including the Bom Jardim Group and the Acampamento Velho Formation, both of which record continental palaeoenvironmental changes in a more than 5000 m thick stratigraphic succession. Age constraints are given by seven Ar‐Ar and U‐Pb determinations on volcanic rocks, which bracket these units between c. 605 and 574 Ma, revealing the best dated and most continuous documented Ediacaran continental succession to date. Depositional systems evolution supports a Phanerozoic‐type glacial context during the last Neoproterozoic glacial event and presents the Picada das Graças Formation (580 ± 3.6 Ma) as the first dated non‐glacial unit coeval to the Gaskiers Formation. 相似文献
4.
Gatan R. Moloto-A-Kenguemba Ricardo I.F. Trindade Patrick Moni Anne Ndlec Roberto Siqueira 《Precambrian Research》2008,164(3-4):214-226
New structural, geochronological and paleomagnetic data were obtained on dolerite dikes of the Nola region (Central African Republic) at the northern border of the Congo craton. In this region, metavolcanic successions were thrust southward onto the craton during the Panafrican orogenic events. Our structural data reveal at least two structural klippes south of the present-day limits of the Panafrican nappe suggesting that it has once covered the whole Nola region, promoting the pervasive hydrothermal greenschist metamorphism observed in the underlying cratonic basement and also in the intrusive dolerite dikes. Paleomagnetic measurements revealed a stable dual-polarity low-inclination magnetization component in nine dikes (47 samples), carried by pyrrhotite and magnetite. This component corresponds to a paleopole at 304.8°E and 61.8°S (dp = 5.4, dm = 10.7) graded at Q = 6. Both metamorphism and magnetic resetting were dated by the 40Ar/39Ar method on amphibole grains separated from the dikes at 571 ± 6 Ma. The Nola pole is the first well-dated paleomagnetic pole for the Congo craton between 580 and 550 Ma. It marks a sudden change in direction of the Congo craton apparent polar wander path at the waning stages of the Panafrican orogenic events. 相似文献
5.
Mário André Trindade Dantas Rodrigo Parisi Dutra Alexander Cherkinsky Daniel Costa Fortier Luciana Hiromi Yoshino Kamino Mario Alberto Cozzuol Adauto de Souza Ribeiro Fabiana Silva Vieira 《Quaternary Research》2013,79(1):61-65
During the Pleistocene a fauna composed of large (biomass > 44 kg) and giant mammals (biomass > 1000 kg) that are usually associated with open environments lived in the Brazilian Intertropical Region. We present here new information concerning the paleoecology and chronology of some species of this megafauna. Carbon isotope analyses were performed for a better understanding of the paleoecology of the species Eremotherium laurillardi (Lund, 1842), Notiomastodon platensis (Ameghino, 1888) and Toxodon platensis (Owen, 1849). The δ13C data allow attributing a generalist diet to these species, which varied according to the kind of habitat in which they lived. In more open habitats all species were grazers; in mixed habitats E. laurillardi and T. platensis were mixed feeders, and N. platensis was grazer; and in more closed habitats all species were mixed feeders. 相似文献
6.
Anne Nédélec Jean‐Louis Paquette Elder Yokoyama Ricardo I. F. Trindade Thierry Aigouy David Baratoux 《Meteoritics & planetary science》2013,48(3):420-431
The Vargeão impact structure was formed in the Serra Geral basaltic and rhyodacitic to rhyolitic lava flows of southern Brazil, that belong to the Paraná‐Etendeka large igneous province. The Chapecó‐type rhyodacites contain small baddeleyite crystals recently dated at 134.3 (±0.8) Ma, which is regarded as the age of this acid volcanism coeval to the flood basalt eruption. Inside the impact structure, a brecciated rhyodacitic sample displays fine veinlets containing numerous lithic fragments in a former melt. This impact breccia contains newly formed zircons, either in the veins or at the contact between a vein and the volcanic matrix. The zircons are 10–50 μm in length, clear and nearly unzoned. In situ laser‐ablation dating of the zircons provides a concordant Early Aptian age of 123.0 ± 1.4 Ma that is regarded as the age of the impact event. As in situ age determination ensures the best possible selection of the analyzed mineral grains, the methodology employed in this study also represents a promising method for dating other impact structures. 相似文献
7.
Jari Nobrega Cardoso Francisco Radler De Aquino Neto Ren Rodrigues Luiz A.F. Trindade 《Organic Geochemistry》1986,10(4-6)
The distributions of polycyclic alkanes were monitored in a Neocomian sequence (well 1-ESS-34) from the Espirito Santo Basin, southeast Brazil. The profiles included, apart from regular hopanes, significant concentrations of 18α(H), 28,30-bisnorhopane and subordinate amounts of gammacerane. Sterane concentrations, normally with hopane/sterane <5, were compatible with other geochemical data indicating a predominantly planktonic/microbial source of the deposited organic matter. Sample maturities ranged from very immature to the onset of oil generation, allowing biomarker distributions to be followed along a broad maturation range. The ability of certain molecular ratios (e.g. C27 17α(H)/17β(H)hopanes) to reflect a maturity sequence with depth in the closely-spaced strata of the immature upper levels (Jiquiá Stage) showed the value of molecular techniques over classical geochemical methods (e.g. vitrinite reflectance) for the study of immature sequences. The presence in the oils of southern Espirito Santo of 28,30-bisnorhopane, gammacerane and methyl steranes in similar concentrations as in extracts of the deepest levels of the 1-ESS-34 well qualify the Jiquia Stage as the probable source rock of oils accumulated in the basin. 相似文献
8.
José Bandeira Ben McGee Afonso C.R. Nogueira Alan S. Collins Ricardo Trindade 《Gondwana Research》2012,21(2-3):323-340
Final Gondwana amalgamation was marked by the closure of the Neoproterozoic Clymene ocean between the Amazonia craton and central Gondwana. The events which occurred in the last stage of this closure were recorded in the upper Alto Paraguai Group in the foreland of the Paraguay orogen. Outcrop-based facies analysis of the siliciclastic rocks of upper Alto Paraguai Group, composed of the Sepotuba and Diamantino Formations, was carried out in the Diamantino region, within the eastern part of the Barra dos Bugres basin, Mato Grosso state, central-western Brazil. The Sepotuba Formation is composed of sandy shales with planar to wave lamination interbedded with fine-grained sandstone with climbing ripple cross-lamination, planar lamination, swaley cross-stratification and tangential to sigmoidal cross-bedding with mud drapes, related to marine offshore deposits. The lower Diamantino Formation is composed of a monotonous, laterally continuous for hundreds of metres, interbedded siltstone and fine-grained sandstone succession with regular parallel lamination, climbing ripple cross-lamination and ripple-bedding interpreted as distal turbidites. The upper part of this formation consists of fine to medium-grained sandstones with sigmoidal cross-bedding, planar lamination, climbing ripple cross-lamination, symmetrical to asymmetrical and linguoid ripple marks arranged in lobate sand bodies. These facies are interbedded with thick siltstone in coarsening upward large-scale cycles related to a delta system. The Sepotuba Formation characterises the last transgressive deposits of the Paraguay basin representing the final stage of a marine incursion of the Clymene ocean. The progression of orogenesis in the hinterland resulted in the confinement of the Sepotuba sea as a foredeep sub-basin against the edge of the Amazon craton. Turbidites were generated during the deepening of the basin. The successive filling of the basin was associated with progradation of deltaic lobes from the southeast, in a wide lake or a restricted sea that formed after 541 ± 7 Ma. Southeastern to east dominant Neoproterozoic source regions were confirmed by zircon grains that yielded ages around 600 to 540 Ma, that are interpreted to be from granites in the Paraguay orogen. This overall regressive succession recorded in the Alto Paraguai Group represents the filling up of a foredeep basin after the final amalgamation of western Gondwana in the earliest Phanerozoic. 相似文献
9.
The Paraguay belt comprises a thick sedimentary succession deposited on the southwestern border of the Amazonian Craton and the Rio Apa Block. The base of the succession in the southern Paraguay belt is marked by a level of glacially derived deposits from the Puga Formation associated with banded iron formations, which has been assumed to be end-Cryogenian in age (635 Ma) by previous authors is spite of the lack of geochronological data. Here we present the first U–Pb SHRIMP ages on detrital zircon grains separated from the matrix of six samples of these diamictites two different localities (Puga Hill and Bodoquena area). U–Pb ages determined from two samples (ca. 130 grains) of Puga Hill show a large variation between 970 Ma and 2100 Ma. Rocks with these ages can be found in the Amazonian Craton suggesting that it is the most probable source of the sediments. Detrital zircons (ca. 230 grains) from the Bodoquena area (about 200 km south of Puga Hill) range from 706 to 1990 Ma. The 1760 Ma source is significantly more important in these samples, comprising more than 70% of analyzed grains, and indicates provenance from the adjacent Rio Apa Block. The youngest zircon was dated at 706 ± 9 Ma, thus constraining the maximum depositional age for the Puga Formation. Possible sources for this younger population could be either the juvenile Mara Rosa magmatic arc in the Brasilia belt, or the rocks from the Laurentian external fold belts located to the west of the sampled area in Neoproterozoic paleogeographic reconstructions. The maximum depositional age of the diamictites (and associated BIFs), together with cap carbonate carbon and strontium isotope data (δ13C = ? 5.0 and 87Sr/86Sr = 0.7077) in Puga Hill, indicate that they were deposited after 700 Ma, suggesting that they may represent the end-Cryogenian event. 相似文献
10.
Pedro Duarte Lídia Silva António Mateus M. Fátima Araújo Mário Reis Romão Trindade Isabel Paiva 《Environmental Earth Sciences》2013,68(2):547-557
The search for suitable sites to install near-surface repositories for low to intermediate level radioactive wastes has increased in the recent years, reflecting both the continuous rise in radioactive materials applications by the society and the increasing awareness of public perception regarding radwaste management. International recommendations towards the application of higher safety standards to low and intermediate level waste disposal sites being developed by the International Atomic Energy Agency (IAEA), and the European Commission decision that each Member State must safely dispose its own radwaste in its territory, according to national radwaste management plans, has leading to new soundly scientific studies. In Portugal, possible locations for that purpose are under study since 2006, following the pre-requisites indicated by IAEA. One of these sites overlaps a significant portion of an ultramafic massif, corresponding to an allochthonous and metamorphosed ophiolite complex. In the surveyed area of this massif, the prevailing rock type consists of (serpentinised) peridotites, occasionally containing irregular bodies of (amphibolitised) gabbros, over which an irregular/ill-developed regolith exists. The activities of 40K, 137Cs, 210Pb, 226Ra and 232Th measured in samples representing three consecutive levels of the regolith upper portion in 13 stations confirm the heterogeneity put in evidence through in situ γ-ray surveys previously performed. The available dataset also demonstrates that radionuclide contents decrease prominently with depth, becoming closer to the bedrock values (up to ca. 41 Bq kg?1 for 40K in flaser-gabbros and near zero for all the remaining cases) but never reaching them. Therefore, the low/moderate radionuclide activity in the regolith upper portion reflect the contribution of sources that are independent of the lithological background; i.e. they indicate external and miscellaneous contributions to the “soil”-forming components, most of them coming from (dry or wet) atmospheric deposition. The chemical composition of the (serpentinised) peridotites and (amphibolitised) gabbros in the surveyed area, as well as their alteration products included in regolith, is homogeneous enough to be used as a faithful reference in monitoring studies of any kind. In addition, the significant 137Cs activities measured in some top “soil” samples (up to 92 Bq kg?1) strongly suggest that there are mineralogical specificities of the peridotite-derived regolith able to fix that radionuclide. This particular feature reinforces the existing criteria that favour the peridotites of Morais as a suitable host for a near surface repository of low to intermediate level radwaste. 相似文献